This invention relates to a leak indicating apparatus for the closed cooling system of an electric machine.
Electric machines of high capacity for example, water power generators, have in recent times been cooled with the aid of a coolant which in most systems is water. The coolant is especially prepared and is circulated in a closed liquid cooling system. Often, there is provided a leak indicating apparatus for detecting undesired losses of coolant because of leaks since such leaks could lead to damage.
A leak indicating apparatus of this type is disclosed in U.S. Pat. No. 3,410,102. In this known apparatus, there are provided transducer elements before and after the parts to be cooled for changing the temperature into an electrical signal. Further, at the highest location of the liquid cooling system, there is provided an expansion tank wherein the liquid level can adjust itself freely and wherein a level measuring device is arranged. This measuring device consists of a floating body arranged in a vertical tube of the expansion tank. The floating body drives a toothed rod in the upward or downward direction according to how the level of the liquid changes. This mechanical operation is initiated by the change of level and is, in turn, translated into an electrical value which corresponds to the level in the expansion tank. This translation is made mechanically with the aid of a toothed wheel which is attached to the movable terminal of a potentiometer, the potentiometer being connected between the plus and minus terminals of a direct current circuit.
Further, between the plus and minus terminals of the direct current circuit, there are provided three series-connected adjustable resistance elements of which two are arranged in front of and behind of the parts of the electric machine which is to be cooled and thereby detect the average temperature and translate the same into an electrical signal since both these resistance elements are wound from a wire material having a resistance value which increases with increasing temperature. In contrast, the third resistance element is essentially independent of the temperature.
The electrical signals indicative of level and temperature changes obtained in the above-described manner are then compared with each other. For this purpose in the known apparatus, the mid-terminal of the temperature-dependent voltage divider and the mid-terminal of the level-dependent voltage divider are connected with each other by means of a relay coil and a diode serially connected with the relay coil. The resistance elements are so adjusted at the normal operating temperature of the electric machine so that the voltage on the relay coil corresponds to zero.
With a change in level in the context of the normal volume-temperature proportionality, the voltage changes on the mid-terminal of the temperature-dependent voltage divider compensate themselves by means of the change of the resistances in front of and behind of the parts to be cooled and, at the midterminal of the level indicating voltage divider by means of a change in level. Therefore, the working contacts of the relay do not close. However, in contrast to the foregoing, if the floating body in the expansion tank should sink because of a leak occurring in the liquid cooling system so that the volume as well as the level no longer corresponds to the normal volume-temperature proportionality, the relay coil is energized and actuates an alarm device with the aid of the working contacts and thereafter, through the working contacts actuates a shutdown mechanism for the electric machine.
The known leak indicating apparatus therefore responds to all volume and level changes corresponding to the non-normal volume-temperature proportionality. This has the disadvantage that the liquid cooling system must be constructed so as to be completely seal-tight, that is, the cooling system may not contain any seals which during operation cause a certain constant coolant loss. Furthermore, the known apparatus requires an available direct current source and individual elements which are precisely matched to each other since direct current potentials must be workable against each other and must be able to be self-compensating.
Siemens-Zeitschrift 1967 discloses a leak indicating apparatus at pages 838 and 839 which also takes into consideration the fact that slide-sealing rings present in the liquid cooling system at rotating machine parts such as pumps have associated therewith a certain coolant loss which must be replaced at definite time intervals. Accordingly, a device for automatically replenishing water is connected to the expansion tank. In the known apparatus, the elevation of the liquid level is detected by means of a level measuring device and this device initiates means for adding replenishing coolant in dependence upon time and level to the expansion tank or it can actuate an indicating device which provides a warning signal. Further, the average temperature of the coolant is measured by means of thermometers which are arranged in back of and in front of the heat exchanger.
In view of the foregoing, it is an object of the invention to provide a leak indicating apparatus which is improved in such a manner that small leaks present in the assembled cooling system with which are associated natural leak losses are not detected by the leak indicating apparatus in the same manner as volume changes caused by temperature changes are not detected.
It is a further object of the invention to provide such a leak indicating apparatus wherein the apparatus can be operated by translating the measured values into electrical signals with direct currents as well as with alternating currents.